//! The language-intelligence seam.
//!
//! The core never speaks a protocol and never blocks. It emits an `lsp` Effect
//! naming a Kind, a file and a byte offset; a shell runs `query` on a worker
//! and posts the answer back as an `lsp_resp` Event. That is the whole async
//! execution model — the same shape the pty readers already use, because a
//! language query is just another thing that answers later.
//!
//! Location answers render as `+Search` rows. A location is
//! `path:LINE:COL text` — or `path:LINE:COL-ENDCOL text` where the protocol
//! answered with a real range, which a look then SELECTS — and that is what
//! look.zig already resolves and what n/N already steps, so a multi-result
//! answer IS helix's picker and a single result IS a jump, with no picker UI
//! written for it. Free text (hover, formatting) rides the same buffer. Rename
//! is the one mutating answer: it emits byte ranges through `edit`, and the core
//! applies them atomically only while the source revision is still current.
//!
//! `query` is the ONLY thing an implementation supplies. Swapping backends is
//! swapping this one function, which is also how the three competing
//! implementations are measured against each other: same core, same harness,
//! same rows, different `query`.
const std = @import("std");

/// What the caller wants to know. The helix command each one backs is named
/// alongside, because the keymap is helix's and these are its verbs.
pub const Kind = enum {
    /// gd
    definition,
    /// gD
    declaration,
    /// gy
    type_definition,
    /// gi
    implementation,
    /// gr
    references,
    /// SPC k
    hover,
    /// SPC s
    document_symbols,
    /// SPC S (arg = the query)
    workspace_symbols,
    /// SPC d, and the list that ]d / [d step
    diagnostics,
    /// SPC D
    workspace_diagnostics,
    /// SPC r (arg = the new name)
    rename,
    /// SPC a
    code_action,
    /// =
    format,
    /// SPC h
    select_refs,
    /// Tab in insert mode, with a `.` immediately before the cursor. NOT an
    /// autocomplete popup — the seam returns locations, so this answers "what
    /// could go here, and where is each of those DEFINED": one row per
    /// candidate, pointing at its declaration, in the same `+Search` buffer
    /// `gr` fills. Nothing is inserted.
    completion,

    // The two introspection kinds. A backend that answers nothing is
    // indistinguishable from a backend that is broken, so these exist to tell
    // those apart — they are the only Kinds whose answer is ABOUT the backend
    // rather than about the code.
    /// SPC l i — configuration, capabilities and the recent-query log
    status,
    /// SPC l w — why the query at the cursor answers what it does. Narrates
    /// the REAL resolution path rather than re-deriving it, so it cannot drift
    /// away from what `gd` actually did.
    explain,

    // What an ANSWER becomes — which buffer it opens, whether a single row
    // jumps instead, whether n/N walk it — is not here: it is one row per Kind
    // in output_pane.traits, beside the same questions asked of `/`, Find,
    // Grep and Help. A Kind added above will not compile until it has one.
};

/// One question. `source` is a snapshot of the buffer taken by the shell
/// before the worker starts — the core keeps editing while this is in flight,
/// so a backend must never reach back into core memory.
pub const Req = struct {
    kind: Kind,
    /// absolute path of the file the offset is in
    path: []const u8,
    /// the buffer's bytes, NUL-terminated (std.zig.Ast and zls both want a
    /// sentinel, and every backend has to parse this same text)
    source: [:0]const u8,
    /// cursor position, a byte offset into `source`
    offset: u32,
    /// kind-specific argument: the new name for a rename, the query for
    /// workspace symbols. Empty otherwise.
    arg: []const u8 = "",
    /// where the project starts — the directory of the pane that asked. A
    /// backend that indexes more than one file walks from here.
    root: []const u8 = "",
};

/// How a row SPELLS a path: relative to `base` if it lives UNDER it, its full
/// absolute self otherwise.
///
/// `base` is `Req.root` — the directory of the file the query was asked about
/// — which is also the directory the results buffer is opened in, so a row
/// shortened here reads as the name that window would have typed and still
/// resolves when looked. `gr` over one file was otherwise the same
/// forty-character absolute prefix repeated down the whole pane, with the part
/// you came to read pushed off the right edge.
///
/// UNDER, not "shorter": a path outside that tree is left absolute rather than
/// walked up to with `../`. An absolute path resolves from anywhere and says
/// where it is; `../../..` says neither, and the moment the row is read
/// somewhere other than beside its own buffer it is wrong.
///
/// This is `look.grep`'s `shown` rule, spelled a second time — see the note
/// there; the two want to become one function.
pub fn rel(base: []const u8, path: []const u8) []const u8 {
    if (base.len == 0) return path;
    const home = std.mem.trimEnd(u8, base, "/");
    if (path.len > home.len and std.mem.startsWith(u8, path, home) and path[home.len] == '/')
        return path[home.len + 1 ..];
    return path;
}

/// Emit one `path:LINE:COL text` row. Line and column are 1-based, the way
/// every other row in a `+Search` buffer is (and the way look.zig parses one).
/// `path` has already been through `rel`: the caller holds the base.
pub fn row(
    out: *std.Io.Writer,
    path: []const u8,
    line: usize,
    col: usize,
    text: []const u8,
) void {
    out.print("{s}:{d}:{d} {s}\n", .{
        path, line + 1, col + 1, std.mem.trim(u8, text, " \t\r\n"),
    }) catch {};
}

/// The same row for a protocol RANGE: `path:LINE:COL-ENDCOL`, which a look
/// SELECTS rather than parking on its first cell — so `gd` lands on the whole
/// name and a references list steps symbol by symbol with each one highlighted
/// (config.range_sep spells the dash; `-` is written out here for the same
/// reason `:` is).
///
/// `end_col` is the protocol's own EXCLUSIVE end character, which is already
/// the 1-based inclusive column pardes wants, so the conversion is the absence
/// of one. A span that is empty or crosses lines falls back to the point row:
/// the only multi-line ranges here are whole declarations, and a goto onto one
/// wants the cursor at its name, not its body painted.
pub fn spanRow(
    out: *std.Io.Writer,
    path: []const u8,
    line: usize,
    col: usize,
    end_line: usize,
    end_col: usize,
    text: []const u8,
) void {
    if (end_line != line or end_col <= col) return row(out, path, line, col, text);
    out.print("{s}:{d}:{d}-{d} {s}\n", .{
        path, line + 1, col + 1, end_col, std.mem.trim(u8, text, " \t\r\n"),
    }) catch {};
}

/// Emit one half-open byte range for a mutating response. Rename is the only
/// current user: every other answer remains human-readable rows. Byte offsets
/// avoid converting the displayed 1-based locations back into source offsets
/// in the core, and the prefix makes malformed or mixed responses fail closed.
pub fn edit(out: *std.Io.Writer, start: usize, end: usize) void {
    out.print("@edit {d} {d}\n", .{ start, end }) catch {};
}

/// Byte offset -> (line, column), both 0-based. Every backend needs it to turn
/// an AST token into a row, so it lives here rather than three times over.
pub fn lineCol(source: []const u8, offset: usize) struct { line: usize, col: usize } {
    const upto = source[0..@min(offset, source.len)];
    const line = std.mem.count(u8, upto, "\n");
    const bol = if (std.mem.lastIndexOfScalar(u8, upto, '\n')) |i| i + 1 else 0;
    return .{ .line = line, .col = upto.len - bol };
}

/// Answer `req`, writing rows to `out`. Runs on a worker thread with no
/// access to the core: everything it may read is in `req`.
///
/// `out` is a plain `std.Io.Writer` — the shell owns the buffer behind it (an
/// `Io.Writer.Allocating`), so a backend never allocates the result, never
/// frees it, and cannot get the allocator wrong. Write failures are the
/// writer's problem; a backend may ignore them.
///
/// `arena` is freed wholesale when the query returns; `gpa` is for a backend's
/// own longer-lived scratch. Errors are not reported — a backend that cannot
/// answer writes nothing, and the core treats "no rows" as "no result", which
/// is also what a language server still starting up looks like.
pub fn query(gpa: std.mem.Allocator, arena: std.mem.Allocator, req: Req, out: *std.Io.Writer) void {
    backend.query(gpa, arena, req, out);
}

/// ZLS, linked in as a module and called directly — no subprocess, no
/// JSON-RPC. See `lsp_zls.zig`. The web shell has no threads, never emits the
/// effect, and cannot build ZLS anyway, so there it is the empty backend the
/// base tree shipped with.
const backend = if (@import("pardes_config").zls_backend) @import("lsp_zls.zig") else struct {
    pub fn query(_: std.mem.Allocator, _: std.mem.Allocator, _: Req, _: *std.Io.Writer) void {}
    pub fn speaks(_: []const u8) bool {
        return false;
    }
    pub const supports: std.EnumSet(Kind) = .initEmpty();
};

/// What this backend can actually answer, for the evaluation harness and for
/// the core (a Kind that is not supported never leaves the keymap). An
/// implementation narrows this to what it really does — claiming a feature it
/// does not have shows up immediately in the harness's matrix.
pub const supports: std.EnumSet(Kind) = backend.supports;

/// Does the backend read this file's LANGUAGE at all? `supports` answers what
/// a backend can do; this answers what it can do it TO, and it exists for the
/// one key that must not be eaten when the answer is no: insert-mode Tab
/// diverts to `completion` after a `.`, so in a README — or in any pane the
/// backend would refuse — it has to indent instead. The core asks rather than
/// knowing, so the list of extensions stays the backend's business.
pub const speaks = backend.speaks;

/// Name shown by the harness and in `SPC ?`. Each implementation renames it.
pub const backend_name = "zls-inproc";