| 1 | package builtin |
| 2 | |
| 3 | import ( |
| 4 | "context" |
| 5 | "encoding/json" |
| 6 | "fmt" |
| 7 | "os" |
| 8 | |
| 9 | "reasonix/internal/diff" |
| 10 | ) |
| 11 | |
| 12 | // preview.go gives the file-writing built-ins the optional tool.Previewer |
| 13 | // capability: compute the change a call would make, reading the current file |
| 14 | // but never writing. A front-end (e.g. a desktop approval card) calls Preview |
| 15 | // before the permission gate runs Execute, so every Preview confines its path |
| 16 | // with confinePreview first: the read must be as bounded as the write. |
| 17 | // |
| 18 | // Each Preview mirrors its Execute's transformation exactly — same arg parsing, |
| 19 | // same uniqueness / not-found rules — so the previewed NewText equals what |
| 20 | // Execute would persist (asserted by TestPreviewMatchesExecute in |
| 21 | // preview_test.go; drift fails the test rather than the preview lying). |
| 22 | |
| 23 | // Preview computes the change write_file would make. A path that does not yet |
| 24 | // exist is a Create; an existing one is a Modify. |
| 25 | func (w writeFile) Preview(ctx context.Context, args json.RawMessage) (diff.Change, error) { |
| 26 | var p struct { |
| 27 | Path string `json:"path"` |
| 28 | Content string `json:"content"` |
| 29 | } |
| 30 | if err := json.Unmarshal(args, &p); err != nil { |
| 31 | return diff.Change{}, fmt.Errorf("invalid args: %w", err) |
| 32 | } |
| 33 | if p.Path == "" { |
| 34 | return diff.Change{}, fmt.Errorf("path is required") |
| 35 | } |
| 36 | p.Path = resolveIn(w.workDir, p.Path) |
| 37 | if err := confinePreview(effectiveWriteRoots(ctx, w.rootSet, w.roots), w.guard, w.managed, p.Path); err != nil { |
| 38 | return diff.Change{}, err |
| 39 | } |
| 40 | |
| 41 | old, kind := "", diff.Create |
| 42 | if src, err := readEditSource(ctx, w.overlay, p.Path); err == nil { |
| 43 | old, kind = src.content, diff.Modify |
| 44 | } else if !os.IsNotExist(err) { |
| 45 | return diff.Change{}, fmt.Errorf("read %s: %w", p.Path, err) |
| 46 | } |
| 47 | return diff.Build(p.Path, old, p.Content, kind), nil |
| 48 | } |
| 49 | |
| 50 | // Preview computes the change edit_file would make. It enforces the same |
| 51 | // "old_string must occur exactly once" rule as Execute, returning that error |
| 52 | // when it doesn't — so a preview never shows a change the call couldn't make. |
| 53 | func (e editFile) Preview(ctx context.Context, args json.RawMessage) (diff.Change, error) { |
| 54 | var p struct { |
| 55 | Path string `json:"path"` |
| 56 | OldString string `json:"old_string"` |
| 57 | NewString string `json:"new_string"` |
| 58 | } |
| 59 | if err := json.Unmarshal(args, &p); err != nil { |
| 60 | return diff.Change{}, fmt.Errorf("invalid args: %w", err) |
| 61 | } |
| 62 | if p.Path == "" { |
| 63 | return diff.Change{}, fmt.Errorf("path is required") |
| 64 | } |
| 65 | if p.OldString == "" { |
| 66 | return diff.Change{}, fmt.Errorf("old_string is required") |
| 67 | } |
| 68 | p.Path = resolveIn(e.workDir, p.Path) |
| 69 | if err := confinePreview(effectiveWriteRoots(ctx, e.rootSet, e.roots), e.guard, e.managed, p.Path); err != nil { |
| 70 | return diff.Change{}, err |
| 71 | } |
| 72 | |
| 73 | src, err := readEditSource(ctx, e.overlay, p.Path) |
| 74 | if err != nil { |
| 75 | return diff.Change{}, fmt.Errorf("read %s: %w", p.Path, err) |
| 76 | } |
| 77 | content := src.content |
| 78 | |
| 79 | applied := applyOldStringEdit(content, p.OldString, p.NewString, false) |
| 80 | switch { |
| 81 | case applied.applied == 1: |
| 82 | // ok |
| 83 | case applied.matches == 0: |
| 84 | return diff.Change{}, oldStringNotFoundError(p.Path, p.OldString, content) |
| 85 | default: |
| 86 | return diff.Change{}, oldStringNotUniqueError(p.Path, p.OldString, content, applied.matches, false) |
| 87 | } |
| 88 | |
| 89 | return diff.Build(p.Path, content, applied.updated, diff.Modify), nil |
| 90 | } |
| 91 | |
| 92 | // Preview computes the change multi_edit would make by replaying every edit |
| 93 | // against an in-memory buffer — exactly as Execute does — and diffing the |
| 94 | // result against the original. Any edit error surfaces here too, so a preview |
| 95 | // of an invalid batch fails the same way the call would. |
| 96 | func (m multiEdit) Preview(ctx context.Context, args json.RawMessage) (diff.Change, error) { |
| 97 | var p struct { |
| 98 | Path string `json:"path"` |
| 99 | Edits []editStep `json:"edits"` |
| 100 | } |
| 101 | if err := json.Unmarshal(args, &p); err != nil { |
| 102 | return diff.Change{}, fmt.Errorf("invalid args: %w", err) |
| 103 | } |
| 104 | if p.Path == "" { |
| 105 | return diff.Change{}, fmt.Errorf("path is required") |
| 106 | } |
| 107 | if len(p.Edits) == 0 { |
| 108 | return diff.Change{}, fmt.Errorf("edits must not be empty") |
| 109 | } |
| 110 | p.Path = resolveIn(m.workDir, p.Path) |
| 111 | if err := confinePreview(effectiveWriteRoots(ctx, m.rootSet, m.roots), m.guard, m.managed, p.Path); err != nil { |
| 112 | return diff.Change{}, err |
| 113 | } |
| 114 | |
| 115 | src, err := readEditSource(ctx, m.overlay, p.Path) |
| 116 | if err != nil { |
| 117 | return diff.Change{}, fmt.Errorf("read %s: %w", p.Path, err) |
| 118 | } |
| 119 | content := src.content |
| 120 | original := content |
| 121 | |
| 122 | for i, step := range p.Edits { |
| 123 | if step.OldString == "" { |
| 124 | return diff.Change{}, fmt.Errorf("edit %d: old_string is required", i+1) |
| 125 | } |
| 126 | result := applyOldStringEdit(content, step.OldString, step.NewString, step.ReplaceAll) |
| 127 | switch { |
| 128 | case result.applied > 0: |
| 129 | content = result.updated |
| 130 | case result.matches == 0: |
| 131 | return diff.Change{}, fmt.Errorf("edit %d: %w", i+1, oldStringNotFoundError(p.Path, step.OldString, content)) |
| 132 | default: |
| 133 | return diff.Change{}, fmt.Errorf("edit %d: %w", i+1, oldStringNotUniqueError(p.Path, step.OldString, content, result.matches, true)) |
| 134 | } |
| 135 | } |
| 136 | return diff.Build(p.Path, original, content, diff.Modify), nil |
| 137 | } |
| 138 |