refactor: switch git blame to incremental output mode

Also, move blame parser and related structures to a new module VcsBlame.

This includes a full parser re-write to take advantage of the slightly
more efficient incremental output format.

src/VcsBlame.zig

@@ -0,0 +1,146 @@
+commits: std.ArrayList(Commit) = .empty,
+lines: std.ArrayList(?u16) = .empty,
+content: std.ArrayList(u8) = .empty,
+
+pub const Commit = struct {
+    // {sha1} {src_line_no} {dst_line_no} {line_count}
+    id: []const u8 = &.{},
+
+    // author {text}
+    author: []const u8 = &.{},
+
+    // author-mail {email}
+    @"author-mail": []const u8 = &.{},
+
+    // author-time {timestamp}
+    @"author-time": i64 = 0,
+
+    // author-tz {TZ}
+    @"author-tz": i16 = 0,
+
+    // committer {text}
+    // committer-mail {email}
+    // committer-time {timestamp}
+    // committer-tz {TZ}
+
+    // summary {text}
+    summary: []const u8 = &.{},
+
+    // previous {sha1} {filename}
+    // filename {filename}
+};
+
+pub fn getLine(self: *const @This(), line: usize) ?*const Commit {
+    if (line >= self.lines.items.len) return null;
+    const commit_no = self.lines.items[line] orelse return null;
+    return &self.commits.items[commit_no];
+}
+
+pub fn addContent(self: *@This(), allocator: std.mem.Allocator, content: []const u8) error{OutOfMemory}!void {
+    return self.content.appendSlice(allocator, content);
+}
+
+pub const Error = error{
+    OutOfMemory,
+    InvalidBlameCommitHash,
+    InvalidBlameCommitSrcLine,
+    InvalidBlameCommitLine,
+    InvalidBlameCommitLines,
+    InvalidBlameHeaderName,
+    InvalidBlameHeaderValue,
+    InvalidBlameLineNo,
+    InvalidBlameLines,
+    InvalidAuthorTime,
+    InvalidAuthorTz,
+};
+
+pub fn parse(self: *@This(), allocator: std.mem.Allocator) Error!void {
+    self.commits.deinit(allocator);
+    self.lines.deinit(allocator);
+    self.commits = .empty;
+    self.lines = .empty;
+
+    var existing: std.StringHashMapUnmanaged(usize) = .empty;
+    defer existing.deinit(allocator);
+
+    const headers = enum { author, @"author-mail", @"author-time", @"author-tz", summary, filename };
+
+    var state: enum { root, commit, headers } = .root;
+    var commit: Commit = .{};
+    var line_no: usize = 0;
+    var lines: usize = 1;
+
+    var it = std.mem.splitScalar(u8, self.content.items, '\n');
+    while (it.next()) |line| {
+        top: switch (state) {
+            .root => {
+                commit = .{};
+                line_no = 0;
+                lines = 0;
+                state = .commit;
+                continue :top .commit;
+            },
+            .commit => { // 35be98f95ca999a112ad3aff0932be766f702e13 141 141 1
+                var arg = std.mem.splitScalar(u8, line, ' ');
+                commit.id = arg.next() orelse return error.InvalidBlameCommitHash;
+                _ = arg.next() orelse return error.InvalidBlameCommitSrcLine;
+                line_no = std.fmt.parseInt(usize, arg.next() orelse return error.InvalidBlameCommitLine, 10) catch return error.InvalidBlameLineNo;
+                lines = std.fmt.parseInt(usize, arg.next() orelse return error.InvalidBlameCommitLines, 10) catch return error.InvalidBlameLines;
+                state = .headers;
+            },
+            .headers => {
+                var arg = std.mem.splitScalar(u8, line, ' ');
+                const name = arg.next() orelse return error.InvalidBlameHeaderName;
+                if (name.len == line.len) return error.InvalidBlameHeaderValue;
+                const value = line[name.len + 1 ..];
+                if (std.meta.stringToEnum(headers, name)) |header| switch (header) {
+                    .author => {
+                        commit.author = value;
+                    },
+                    .@"author-mail" => {
+                        commit.@"author-mail" = value;
+                    },
+                    .@"author-time" => {
+                        commit.@"author-time" = std.fmt.parseInt(@TypeOf(commit.@"author-time"), value, 10) catch return error.InvalidAuthorTime;
+                    },
+                    .@"author-tz" => {
+                        commit.@"author-tz" = std.fmt.parseInt(@TypeOf(commit.@"author-tz"), value, 10) catch return error.InvalidAuthorTz;
+                    },
+                    .summary => {
+                        commit.summary = value;
+                    },
+                    .filename => {
+                        line_no -|= 1;
+                        const to_line_no = line_no + lines;
+                        const commit_no: usize = if (existing.get(commit.id)) |n| n else blk: {
+                            const n = self.commits.items.len;
+                            try existing.put(allocator, commit.id, self.commits.items.len);
+                            (try self.commits.addOne(allocator)).* = commit;
+                            break :blk n;
+                        };
+                        if (self.lines.items.len < to_line_no) {
+                            try self.lines.ensureTotalCapacity(allocator, to_line_no);
+                            while (self.lines.items.len < to_line_no)
+                                (try self.lines.addOne(allocator)).* = null;
+                        }
+                        for (line_no..to_line_no) |ln|
+                            self.lines.items[ln] = @intCast(commit_no);
+
+                        state = .root;
+                    },
+                };
+            },
+        }
+    }
+}
+
+pub fn reset(self: *@This(), allocator: std.mem.Allocator) void {
+    self.commits.deinit(allocator);
+    self.lines.deinit(allocator);
+    self.content.deinit(allocator);
+    self.commits = .empty;
+    self.lines = .empty;
+    self.content = .empty;
+}
+
+const std = @import("std");