55 lines
2.5 KiB
Markdown
55 lines
2.5 KiB
Markdown
# FlagPole Specifications
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This document describes the current technical specifications and architecture of the FlagPole feature flagging library.
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## Core Concepts
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### Flag
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An immutable data object representing a feature flag and its evaluation strategies.
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- **Properties**:
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- `name` (string): Unique identifier.
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- `enabled` (bool|null): Explicit override. If `true`/`false`, evaluation stops here.
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- `rolloutPercentage` (int|null): 0-100 value for gradual rollout.
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- `allowList` (list<string>): Keys that always receive `true`.
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- `rules` (list<Rule>): Complex attribute-based targeting rules.
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- `targetingKey` (string|null): Optional override for the attribute used in rollout/allowList.
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### Context
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A container for attributes (e.g., `userId`, `email`, `userGroup`) used during evaluation.
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- **Targeting Keys**: By default, the evaluator looks for `key`, `userId`, `id`, or `email` (in that order), unless overridden by `Flag->targetingKey`.
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### Evaluator
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The engine that applies flag strategies against a context.
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- **Precedence**:
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1. `allowList`: If the targeting key is in the list, return `true`.
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2. `enabled`: If non-null, return its boolean value.
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3. `rules`: If any rule matches the context attributes, return `true`.
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4. `rolloutPercentage`: Hash-based stable bucketing (0-99).
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5. `fallback`: Returns the user-provided default.
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### FeatureManager
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The main entry point for the consumer.
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- **Method**: `isEnabled(string $flagName, ?Context $context = null, bool $default = false): bool`
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- **Logging**: Supports PSR-3 logging of evaluation reasons.
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## Technical Details
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### Rollout Hashing
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- Algorithm: `xxh3(flagName + ":" + targetingKey)`.
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- Normalization: `hexdec(substr(hash, 0, 8)) % 100`.
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- Bucketing: 0-99.
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### Repositories
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- `FlagRepositoryInterface`: Defines `get(string $name)` and `all()`.
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- `InMemoryFlagRepository`: Provided for testing and simple setups.
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- `JsonFileRepository`: Loads flags from a JSON file. Now supports lazy-loading hydration for better performance.
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### FlagHydrator
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A dedicated component responsible for transforming raw configuration arrays into validated `Flag` and `Rule` objects.
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- **Validation**: Ensures all rules have required fields and valid operators (`eq`, `neq`, `gt`, `gte`, `lt`, `lte`, `in`, `nin`, `contains`).
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- **Reuse**: Used by both `InMemoryFlagRepository` and `JsonFileRepository` to ensure consistent flag creation.
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## Constraints
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- PHP 8.2+ required.
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- No external dependencies (PSR interfaces excepted in future).
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