//! `cph-check` — check-pipeline orchestration.
//!
//! Owned by **WU-5**. Ties together `cph-model` (load), `cph-schema`
//! (validate), and `cph-typst` (compile), runs the render-coverage rule
//! (ADR-0005's "missing render ⇒ warning"), and collects all diagnostics.
//!
//! The orchestrator owns *sequencing and gating*, not the individual checks:
//! each phase is implemented by an upstream crate, and `cph-check` decides the
//! order, what gates what, and how the results are merged / deduped. See
//! [`check`] for the full pipeline and [`build`] for the export path.

use std::path::Path;

use cph_diag::{DiagCode, Diagnostic, Severity};
use cph_typst::Engine;

/// The default render target when a lesson declares no `[targets.*]` at all.
const DEFAULT_TARGET: &str = "student";

/// Severity of the render-coverage ("element ignored under a target") diagnostic.
///
/// **PINNED to `warning` by the contract.** Mirrors the Lean master's
/// `Spec.Courseware.renderIgnoredSeverity : Severity := .warning`
/// (`spec/Spec/Courseware/Check/Diagnostic.lean`), itself citing ADR-0005: when a
/// `(kind, target)` pair has no render rule the checker reports that the element
/// is ignored under that target and **does not block the export**. Naming the
/// severity as a const makes "it is a warning, not an error" a greppable,
/// alignable fact rather than an inline literal.
const RENDER_IGNORED_SEVERITY: Severity = Severity::Warning;

/// The result of running [`check`] (or the check phases of [`build`]).
#[derive(Debug, Clone, PartialEq)]
pub struct CheckReport {
    /// Every diagnostic collected across all phases, deduplicated.
    pub diagnostics: Vec<Diagnostic>,
    /// `false` if `cph_model::load` returned `None` (a hard manifest failure
    /// that prevents any further phase from running).
    pub lesson_loaded: bool,
}

impl CheckReport {
    /// How many collected diagnostics are `Error`-severity.
    pub fn error_count(&self) -> usize {
        self.diagnostics
            .iter()
            .filter(|d| d.severity == Severity::Error)
            .count()
    }

    /// How many collected diagnostics are `Warning`-severity.
    pub fn warning_count(&self) -> usize {
        self.diagnostics
            .iter()
            .filter(|d| d.severity == Severity::Warning)
            .count()
    }

    /// Whether any collected diagnostic is `Error`-severity.
    ///
    /// **Legality decision (spec alignment).** `!has_errors()` is the
    /// implementation of `Spec.Courseware.Legal` (`spec/Spec/Courseware/Check/Diagnostic.lean`):
    /// a lesson is *legal* iff its diagnostics contain no error-level diagnostic
    /// (warnings are non-blocking — see `Severity` / ADR-0010). There is no CI
    /// gate enforcing this alignment (repo constitution); it is kept greppable
    /// here so a reviewer can tie the orchestrator's gate to the Lean master.
    pub fn has_errors(&self) -> bool {
        self.diagnostics
            .iter()
            .any(|d| d.severity == Severity::Error)
    }
}

/// Run the full check pipeline against the engineering file at `root`.
///
/// Phases, in order, with gating:
/// - **(a) load** — `cph_model::load`. Its diagnostics are collected. On a hard
///   failure (`None`) the report is returned immediately with
///   `lesson_loaded == false`; nothing downstream can run.
/// - **(b) structural** — for each part, check `part.kind` is in
///   `cph_schema::known_kinds()`; an unknown kind is an `UnknownKind` error.
///   (cph-model already checked path existence, `..` traversal, and
///   part/element kind *mismatch*; this complements that with the *known-set*
///   check and does not duplicate it.) Parts whose folder cph-model already
///   flagged as missing are skipped for the rest of the pipeline.
/// - **(c) schema** — for each part whose folder exists and whose kind is
///   known, `cph_schema::validate(&part.descriptor)`.
/// - **(d) typst compile** — only if phases (a)–(c) produced **zero** errors
///   (otherwise the compile is noise on known-broken input). Compiles each
///   declared `lesson.targets` (defaulting to `"student"` if none), deduping
///   identical diagnostics across targets.
/// - **(e) render-coverage** — a `warning` (never an error) for each
///   `(kind, target)` the target's `covers` declaration does not include. Runs
///   regardless of (d) gating.
///
/// The engine is taken as a parameter so the caller owns it (and tests can
/// inject `Engine::with_render_dir`).
pub fn check(root: &Path, engine: &Engine) -> CheckReport {
    let mut diags = Vec::new();

    // (a) load.
    let (lesson, load_diags) = cph_model::load(root);
    diags.extend(load_diags);

    let Some(lesson) = lesson else {
        // Hard manifest failure: nothing else can run.
        return CheckReport {
            diagnostics: dedup(diags),
            lesson_loaded: false,
        };
    };

    let known = cph_schema::known_kinds();

    // (b) structural + (c) schema.
    run_structural_and_schema(&lesson, known, &mut diags);

    // (d) typst compile — gated on zero errors from (a)–(c).
    let pre_compile_has_error = diags.iter().any(|d| d.severity == Severity::Error);
    if !pre_compile_has_error {
        for target in compile_targets(&lesson) {
            diags.extend(engine.compile_check(&lesson, target));
        }
    }

    // (e) render-coverage — always runs; only a warning. Skips parts already
    // broken in (b) (missing folder / unknown kind).
    diags.extend(render_coverage(&lesson, known));

    CheckReport {
        diagnostics: dedup(diags),
        lesson_loaded: true,
    }
}

/// Build a PDF for `target`.
///
/// Runs the check phases **(a)–(c)** (load → structural → schema). If those
/// produce any `Error`, the build is refused: returns `(None, report)` with the
/// blocking diagnostics. Otherwise it compiles + exports the PDF for `target`
/// via `engine.build_pdf`; on a clean compile returns `(Some(bytes), report)`,
/// and on a typst error returns `(None, report)` with the compile diagnostics
/// folded into the report.
///
/// Note `build` does **not** run render-coverage (phase (e)): coverage warnings
/// describe export *loss*, which is informational for a `check`, not a gate on
/// producing a single target's PDF.
pub fn build(root: &Path, engine: &Engine, target: &str) -> (Option<Vec<u8>>, CheckReport) {
    let mut diags = Vec::new();

    // (a) load.
    let (lesson, load_diags) = cph_model::load(root);
    diags.extend(load_diags);

    let Some(lesson) = lesson else {
        return (
            None,
            CheckReport {
                diagnostics: dedup(diags),
                lesson_loaded: false,
            },
        );
    };

    let known = cph_schema::known_kinds();

    // (b) structural + (c) schema.
    run_structural_and_schema(&lesson, known, &mut diags);

    if diags.iter().any(|d| d.severity == Severity::Error) {
        return (
            None,
            CheckReport {
                diagnostics: dedup(diags),
                lesson_loaded: true,
            },
        );
    }

    // Phases passed: compile + export the requested target.
    match engine.build_pdf(&lesson, target) {
        Ok(bytes) => (
            Some(bytes),
            CheckReport {
                diagnostics: dedup(diags),
                lesson_loaded: true,
            },
        ),
        Err(compile_diags) => {
            diags.extend(compile_diags);
            (
                None,
                CheckReport {
                    diagnostics: dedup(diags),
                    lesson_loaded: true,
                },
            )
        }
    }
}

/// One shell step's execution outcome (for [`run_shell_target`]).
#[derive(Debug, Clone, PartialEq)]
pub struct ShellStepOutcome {
    /// The command line that was run (verbatim from the manifest `run` field).
    pub run: String,
    /// Process exit code (`None` if the process was killed by a signal).
    pub status: Option<i32>,
    /// Captured stdout.
    pub stdout: String,
    /// Captured stderr.
    pub stderr: String,
}

impl ShellStepOutcome {
    /// Whether the step exited successfully (status 0).
    pub fn ok(&self) -> bool {
        self.status == Some(0)
    }
}

/// The result of [`run_shell_target`].
#[derive(Debug, Clone, PartialEq)]
pub struct ShellRunReport {
    /// The check phases' report (load → structural → schema). Shell steps run
    /// only when this has no errors.
    pub check: CheckReport,
    /// Each shell step's outcome, in declared order. Empty if the build was
    /// refused (check errors, unknown target, or the target has no shell steps).
    pub outcomes: Vec<ShellStepOutcome>,
    /// `true` if the target was found, check passed, and every shell step exited 0.
    pub ok: bool,
}

/// Execute the `Shell` steps of a `file-tree`/tool-generated target (ADR-0009
/// category (b); e.g. the KenKen interactives produced by the `kendoku` CLI).
///
/// This is the **escape-hatch executor**: unlike [`build`] (which compiles a
/// typst template to a PDF), a shell target hands off to an external tool that
/// writes files itself. cph only *runs the declared command* in the engineering
/// root and reports what happened — it assembles nothing.
///
/// Contract / safety:
/// - Runs the check phases first (load → structural → schema). Any error refuses
///   the run (`ok == false`, no command executed) — a shell build of a broken
///   lesson is not attempted.
/// - Each `Step::Shell { run }` is executed via the platform shell
///   (`sh -c <run>` / `cmd /C <run>`) with the **engineering root as the working
///   directory**, so a manifest can use root-relative paths.
/// - **Arbitrary command execution is opt-in by construction**: this function is
///   only reached from `cph build --target <name>`, never from `check`. Callers
///   (the CLI) surface the command before running it.
/// - `TypstCompile` steps inside the same target are skipped here (a shell target
///   is not a typst build); a target with no shell steps yields `ok == false`.
pub fn run_shell_target(root: &Path, engine: &Engine, target: &str) -> ShellRunReport {
    let mut diags = Vec::new();

    let (lesson, load_diags) = cph_model::load(root);
    diags.extend(load_diags);

    let Some(lesson) = lesson else {
        return ShellRunReport {
            check: CheckReport {
                diagnostics: dedup(diags),
                lesson_loaded: false,
            },
            outcomes: Vec::new(),
            ok: false,
        };
    };

    let known = cph_schema::known_kinds();
    run_structural_and_schema(&lesson, known, &mut diags);

    // Suppress the unused-parameter warning while keeping the signature uniform
    // with `build`/`check` (the engine is not needed to run shell steps, but
    // callers pass it so the API is consistent and future steps may use it).
    let _ = engine;

    let has_error = diags.iter().any(|d| d.severity == Severity::Error);

    let Some(tc) = lesson.targets.iter().find(|t| t.name == target) else {
        diags.push(
            Diagnostic::error(
                DiagCode::SchemaViolation,
                format!("target '{target}' not declared in manifest"),
            )
            .with_hint(format!(
                "add a `[targets.{target}]` table, or run a declared target"
            )),
        );
        return ShellRunReport {
            check: CheckReport {
                diagnostics: dedup(diags),
                lesson_loaded: true,
            },
            outcomes: Vec::new(),
            ok: false,
        };
    };

    let shell_steps: Vec<&str> = tc
        .steps
        .iter()
        .filter_map(|s| match s {
            cph_model::Step::Shell { run } => Some(run.as_str()),
            cph_model::Step::TypstCompile { .. } => None,
        })
        .collect();

    if has_error || shell_steps.is_empty() {
        return ShellRunReport {
            check: CheckReport {
                diagnostics: dedup(diags),
                lesson_loaded: true,
            },
            outcomes: Vec::new(),
            ok: false,
        };
    }

    // Run each shell step in the engineering root. First non-zero exit stops the
    // sequence (a failed step's successors likely depend on it).
    let mut outcomes = Vec::new();
    let mut all_ok = true;
    for run in shell_steps {
        let outcome = run_one_shell(&lesson.root, run);
        let ok = outcome.ok();
        outcomes.push(outcome);
        if !ok {
            all_ok = false;
            break;
        }
    }

    ShellRunReport {
        check: CheckReport {
            diagnostics: dedup(diags),
            lesson_loaded: true,
        },
        outcomes,
        ok: all_ok,
    }
}

/// Whether the named target is a **shell-step** target (its steps contain at
/// least one `Step::Shell` and no `Step::TypstCompile`) — i.e. a tool-generated
/// asset bundle that [`run_shell_target`] executes rather than [`build`]
/// compiling to PDF.
///
/// Loads the lesson read-only (ignoring diagnostics); an unloadable lesson or an
/// unknown target returns `false`, so the caller falls through to the normal
/// (typst) build path, which then reports the real error.
pub fn target_is_shell(root: &Path, target: &str) -> bool {
    let (Some(lesson), _) = cph_model::load(root) else {
        return false;
    };
    lesson
        .targets
        .iter()
        .find(|t| t.name == target)
        .is_some_and(|t| {
            t.steps.iter().any(|s| matches!(s, cph_model::Step::Shell { .. }))
                && !t.steps.iter().any(|s| matches!(s, cph_model::Step::TypstCompile { .. }))
        })
}

/// Run one shell command line in `cwd` via the platform shell, capturing output.
fn run_one_shell(cwd: &Path, run: &str) -> ShellStepOutcome {
    use std::process::Command;

    let output = if cfg!(target_os = "windows") {
        Command::new("cmd").arg("/C").arg(run).current_dir(cwd).output()
    } else {
        Command::new("sh").arg("-c").arg(run).current_dir(cwd).output()
    };

    match output {
        Ok(out) => ShellStepOutcome {
            run: run.to_string(),
            status: out.status.code(),
            stdout: String::from_utf8_lossy(&out.stdout).into_owned(),
            stderr: String::from_utf8_lossy(&out.stderr).into_owned(),
        },
        Err(e) => ShellStepOutcome {
            run: run.to_string(),
            status: None,
            stdout: String::new(),
            stderr: format!("failed to spawn command: {e}"),
        },
    }
}

/// Whether a part's folder exists on disk. cph-model emits `PartPathMissing`
/// for parts whose folder is absent, so the orchestrator skips those parts in
/// the structural/schema/coverage phases to avoid piling diagnostics on the
/// same root cause.
fn part_exists(p: &cph_model::Part) -> bool {
    p.descriptor.dir.is_dir()
}

/// Phases (b) + (c): the known-kind structural check and per-part schema
/// validation. Shared by [`check`] and [`build`] so their gating stays
/// identical.
fn run_structural_and_schema(
    lesson: &cph_model::Lesson,
    known: &[&str],
    diags: &mut Vec<Diagnostic>,
) {
    // (b) structural: known-kind check.
    for part in &lesson.parts {
        if !part_exists(part) {
            continue;
        }
        if !known.contains(&part.kind.as_str()) {
            diags.push(
                Diagnostic::error(
                    DiagCode::UnknownKind,
                    format!(
                        "part '{}' has unknown kind '{}'",
                        part.path.display(),
                        part.kind
                    ),
                )
                .with_hint(format!("valid kinds are: {}", known.join(", "))),
            );
        }
    }

    // (c) schema: validate each existing part with a known kind. Skipping
    // unknown kinds avoids a second `UnknownKind` from `cph_schema::validate`
    // (already reported in (b)).
    for part in &lesson.parts {
        if !part_exists(part) || !known.contains(&part.kind.as_str()) {
            continue;
        }
        diags.extend(cph_schema::validate(&part.descriptor));
    }
}

/// The targets to compile-check for [`check`]: every declared **typst-compile**
/// target, or `["student"]` if the lesson declares none.
///
/// A target whose steps are all `Shell` (e.g. a tool-generated asset bundle —
/// ADR-0005 category (b), like the KenKen interactives produced by `kendoku`) is
/// **not** typst-compiled, so it is excluded here: compile-checking it would
/// wrongly route a non-typst build through the typst engine. Such targets are
/// executed only on an explicit `cph build --target <name>` (see
/// [`run_shell_target`]); `check` validates the lesson structure, not the
/// outcome of running an external tool.
fn compile_targets(lesson: &cph_model::Lesson) -> Vec<&str> {
    if lesson.targets.is_empty() {
        return vec![DEFAULT_TARGET];
    }
    lesson
        .targets
        .iter()
        .filter(|t| t.steps.iter().any(|s| matches!(s, cph_model::Step::TypstCompile { .. })))
        .map(|t| t.name.as_str())
        .collect()
}

/// Phase (e): for each `(part.kind, target)` over the lesson's declared targets,
/// emit a `RenderIgnored` **warning** when the target does not cover that kind.
///
/// Coverage is the per-target **declaration** ADR-0011 pinned (and the spec's
/// `RenderConfig.covers k t` in `Export/Render.lean`): a target's
/// `cph_model::TargetConfig::covers` lists the kinds it renders. A used kind not
/// in that list draws the warning. An **absent** `covers` (the loader's `None`)
/// is resolved here — the orchestrator owns the kind universe via `cph-schema` —
/// to "covers all known kinds", so an undeclared target is fully covering rather
/// than covering nothing. (An explicit `covers = []` stays empty: it covers
/// nothing on purpose.) Parts already broken in (b) (missing folder / unknown
/// kind) are skipped — they are reported there.
fn render_coverage(lesson: &cph_model::Lesson, known: &[&str]) -> Vec<Diagnostic> {
    let mut out = Vec::new();
    // De-dupe (kind, target) pairs so we emit one warning per pair, not per part.
    let mut seen: Vec<(String, String)> = Vec::new();

    for part in &lesson.parts {
        // Skip parts already flagged structurally.
        if !part_exists(part) || !known.contains(&part.kind.as_str()) {
            continue;
        }
        for target in &lesson.targets {
            // Resolve the coverage set: an absent declaration defaults to the
            // full known-kind universe; an explicit list (possibly empty) is
            // taken verbatim.
            let covered = match &target.covers {
                None => true,
                Some(kinds) => kinds.iter().any(|k| k == &part.kind),
            };
            if covered {
                continue;
            }
            let key = (part.kind.clone(), target.name.clone());
            if seen.contains(&key) {
                continue;
            }
            seen.push(key);
            let mut d = Diagnostic::warning(
                DiagCode::RenderIgnored,
                format!(
                    "kind '{}' is not covered by target '{}'; it will be omitted from that export",
                    part.kind, target.name
                ),
            )
            .with_hint(format!(
                "add '{}' to `covers` under target '{}', or remove the target",
                part.kind, target.name
            ));
            // Pin the severity via the named contract const. `Diagnostic::warning`
            // already produces a warning, but assigning the const keeps the
            // alignment to `renderIgnoredSeverity` load-bearing and greppable.
            d.severity = RENDER_IGNORED_SEVERITY;
            out.push(d);
        }
    }
    out
}

/// Deduplicate diagnostics that are identical (same code+severity+message+span+
/// hint). The same typst error can surface once per compiled target, and the
/// same root cause can be reached by more than one phase; callers see each
/// distinct problem once.
fn dedup(diags: Vec<Diagnostic>) -> Vec<Diagnostic> {
    let mut out: Vec<Diagnostic> = Vec::with_capacity(diags.len());
    for d in diags {
        if !out.contains(&d) {
            out.push(d);
        }
    }
    out
}